Residual current circuit breakers (RCCBs) are components for implementing the protective measure of protection by automatically switching off the power supply in accordance with the requirements of VDE 0100 Part 410 or corresponding international installation regulations. Devices in the DFS 4 series are compact two- or four-pole residual current circuit breakers. In the standard version, they only take up four division units. While the DFS 4 version for alternating and pulsating direct residual currents is designed for three-phase networks, but can also be used in single-phase networks, there are special versions for single- or three-phase operation in the universal current sensitive versions (type B, type B+). Despite the compact dimensions, a large number of different tripping currents and characteristics are available for rated currents - depending on the version - up to 125 A. All devices are available in the HD version, which is particularly suitable for use in harsh environments (tunnels, swimming pools, etc.). They also have large double-deck terminals for accommodating large conductor cross-sections, a practical multi-function switch toggle and can be labeled with pre-made labels using free software. DFS 2 and DFS 4 with residual current characteristic B detect smooth DC residual currents as well as all other residual currents of type B in accordance with IEC 60755. The operating voltage required for this is taken from the mains voltage. Correct voltage supply is guaranteed if the voltage between the mains conductors is ? 50 V. Type A residual currents are detected regardless of the mains voltage. Furthermore, these residual current circuit breakers detect residual currents of all frequencies up to 100 kHz without gaps. With this large frequency range of residual current detection, they significantly exceed the requirements of the construction standards for type B residual current circuit breakers. Fault protection in accordance with VDE 0100 Part 410 is provided over the entire frequency range of residual current detection with an appropriate earth resistance. The maximum permissible earthing resistance is calculated as the quotient of the permissible contact voltage and the highest tripping fault current in the entire recorded frequency range. For residual current circuit breakers with the NK characteristic, the tripping frequency response is below the human tolerance limit for damage caused by body currents at different frequencies. For RCCBs with a rated residual current of 30 mA, this means that extensive personal protection is achieved even with fault currents above the rated frequency. With an upper tripping threshold of 300 mA at frequencies up to 100 kHz, significantly more sensitive and far-reaching protection against fire-hazardous earth fault currents is provided compared to the B SK or B+ characteristics. This means that comprehensive fire protection is also possible for electronic equipment with high clock frequencies.The high level of protection provided by the NK characteristic requires the system to be monitored to be designed with low leakage current. Selective residual current circuit breakers require a longer flow time of the fault current to be triggered than instantaneous switches. This enables selective shutdown in systems with staggered distributions, ie with series-connected RCCBs, in the event of a fault only the RCCB in whose immediately downstream system section the earth fault occurs will trip. Due to their long shutdown times and high rated residual currents, selective residual current circuit breakers only provide fire protection and fault protection (protection against indirect contact). Additional protection (protection against direct contact, personal protection) is therefore not possible.Standard devices are designed for monitoring circuits with a rated voltage of 230 V or 400 V and a rated frequency of 50 Hz.Features: selective to all undelayed RCCBs (type AC, A or B) for residual currents of all frequencies in the detection range